[linux-pm] [RFC][PATCH 0/2 -mm] kexec based hibernation -v3
huang.ying.caritas at gmail.com
Fri Sep 21 09:44:57 EDT 2007
On 9/21/07, Mika Penttilä <mika.penttila at kolumbus.fi> wrote:
> > Usage:
> > 1. Compile kernel with following options selected:
> > CONFIG_X86_32=y
> > CONFIG_RELOCATABLE=y # not needed strictly, but it is more convenient with it
> > CONFIG_KEXEC=y
> > CONFIG_CRASH_DUMP=y # only needed by kexeced kernel to save/restore memory image
> > CONFIG_PM=y
> > CONFIG_KEXEC_JUMP=y
> > 2. Download the kexec-tools-testing git tree, apply the kexec-tools
> > kjump patches (or download the source tar ball directly) and
> > compile.
> > 3. Download and compile the krestore tool.
> > 4. Prepare 2 root partition used by kernel A and kernel B/C, referred
> > as /dev/hda, /dev/hdb in following text. This is not strictly
> > necessary, I use this scheme for testing during development.
> > 5. Boot kernel compiled for normal usage (kernal A).
> > 6. Load kernel compiled for hibernating/restore usage (kernel B) with
> > kexec, the same kernel as that of 5 can be used if
> > CONFIG_RELOCATABLE=y and CONFIG_CRASH_DUMP=y are selected.
> > The --elf64-core-headers should be specified in command line of
> > kexec, because only the 64bit ELF is supported by krestore tool.
> > For example, the shell command line can be as follow:
> > kexec -p -n /boot/bzImage --mem-min=0x100000 --mem-max=0xffffff
> > --elf64-core-headers --append="root=/dev/hdb single"
> > 7. Jump to the hibernating kernel (kernel B) with following shell
> > command line:
> > kexec -j
> > 8. In the hibernating kernel (kernel B), the memory image of
> > hibernated kernel (kernel A) can be saved as follow:
> > cp /proc/vmcore .
> > cp /sys/kernel/kexec_jump_back_entry .
> Here we save also kernel B's pages.
No, the kernel B's pages will not be saved. Because when we build the
elfcore (/proc/vmcore) header, we exclude memory area used by kernel
B. The details can be found in kexec-tools patches.
> > 9. Shutdown or reboot in hibernating kernel (kernel B).
> > 10. Boot kernel (kernel C) compiled for hibernating/restore usage on
> > the root file system /dev/hdb in memory range of kernel B.
> > For example, the following kernel command line parameters can be
> > used:
> > root=/dev/hdb single memmap=exactmap memmap=640K at 0K memmap=15M at 1M
> 0-640K from kernel A overrides 0-640K of kernel C at restore time.
No. The 0-640K is not in the memory image of kernel A. It is excluded
from memory image of kernel A in /sbin/kexec. Not very strictly, there
is one backup page for each page in 0-640K, after jump back, the
backup page will be swapped with the target page (in 0-640K). No
information is lost. So you can jump back and forth, for arbitrary
> > 11. In restore kernel (kernel C), the memory image of kernel A can be
> > restored as follow:
> > cp kexec_jump_back_entry /sys/kernel/kexec_jump_back_entry
> > krestore vmcore
> This steps replaces kernel C's pages with kernel B's (at least 15m-16m),
> saved at step 8, so these kernels should be equal? Or they must be
> physically located in non-overlapping regions such that C is in B's
> memory range but non-overlapping. The proposed setup doesn't guaratee
> this afaics.
No. These pages are excluded from /proc/vmcore. These kernels need not
to be equal.
> > 12. Jump back to hibernated kernel (kernel A)
> > kexec -b
More information about the kexec